Selective functionalization of chiral ferrocenyl acetals. Easy access to various tri- and tetrasubstituted ferrocenes with controlled geometry

Article abstract of DOI:10.1021/om020462g

The lithiation of 2-substituted chiral dioxane 2, followed by electrophilic trapping of the lithiated intermediate, yields various 1,5-disubstitued acetals with good yields and excellent control of the geometry. These acetals can be easily hydrolyzed into

Full text of DOI:10.1021/om020462g

4552
Organometallics 2002, 21, 4552-4555
Notes
Selective F u n ction a liza tion of Ch ir a l F er r ocen yl Aceta ls.
Ea sy Access to Va r iou s Tr i- a n d Tetr a su bstitu ted
F er r ocen es w ith Con tr olled Geom etr y
J e´roˆme Chiffre, Yannick Coppel, Gilbert G. A. Balavoine,
J ean-Claude Daran, and Eric Manoury*
Laboratoire de Chimie de Coordination, 205 Route de Narbonne,
F-31077 Toulouse Cedex, France
Received J une 10, 2002
Summary: The lithiation of 2-substituted chiral dioxane
2, followed by electrophilic trapping of the lithiated
intermediate, yields various 1,5-disubstitued acetals with
good yields and excellent control of the geometry. These
acetals can be easily hydrolyzed into various 1,5-disub-
stitued ferrocenecarboxaldehydes (in an enantiomerically
pure form if the two substituents are different), which
can be furthermore substituted on the other Cp ring to
yield unprecedented 2,5,1′-ferrocenecarboxaldehydes (in
an enantiomerically pure form if they are chiral). The
three substituents on ferrocenecarboxaldehyde can be
different: this is, to the best of our knowledge, the first
example of enantiomerically pure 1,2,3,1′-tetrasubsti-
tuted ferrocene with planar chirality only.
lithiations of nonchiral monosubstituted ferrocenes
(direct methods) using chiral tertiary amines as addi-
tives, to obtain disubstituted ferrocenes with sometimes
very high enantioselectivities (up to 99% ee), have been
recently developed.10 In addition, more complex substi-
tution patterns are now available in an enantiomerically
pure form: 1,2,1′- or 1,2,3-trisubstituted,4d,6a,11,12 1,2,1′,2′-
tetrasubstituted,11e,f,13 or very recently 1,2,3,1′,2′,3′-
(4) (a) Sokolov, V. I.; Troitskaya, L. L.; Reutov, O. A. J . Organomet.
Chem. 1979, 182, 537-546. (b) Lopez, C.; Bosque, R.; Solans, X.; Font-
Bardia, M. Tetrahedron: Asymmetry 1996, 7, 2527-2530. (c) Wildham,
M.; Mereiter, K.; Bourghida, M. Tetrahedron: Asymmetry 1998, 9,
2983-2986. (d) Ganter, C.; Wagner, T. Chem. Ber. 1995, 128, 1157-
1161. (e) Kitzler, R.; Xiao, L.; Weissensteiner, W. Tetrahedron: Asym-
metry 2000, 11, 3459-3462.
(5) (a) Riant, O.; Samuel, O.; Kagan, H. B. J . Am. Chem. Soc. 1993,
115, 5835-5836. (b) Riant, O.; Samuel, O.; Flessner, T.; Taudien, S.;
Kagan, H. B. J . Org. Chem. 1997, 62, 6733-6745.
In tr od u ction
The need for efficient synthesis of various ferrocene
derivatives drastically increased in the last 10 years
because of the booming use of such compounds in
numerous fields of science.1 Indeed, in some applications
such as materials science or asymmetric catalysis, an
efficient access to ferrocenes with a controlled planar
chirality is of great interest. Since the pioneering work
of Ugi,3 many efficient methods to obtain enantiomeri-
cally pure 1,2-disubstituted ferrocenes have been de-
veloped.2 Most of them are based on diastereoselective
orthometalation of ferrocenyl derivatives containing
chiral directing groups. These directing groups may be
tertiary amine,3,4 acetal,5 sulfoxide,6 imine,7 oxazoline,8
or more recently phosphine oxide.9 To avoid the some-
times tedious work of synthesizing ferrocenes bearing
a chiral directing group, several enantioselective ortho-
(6) (a) Rebie`re, F.; Riant, O.; Ricard, L.; Kagan H. B. Angew. Chem.,
Int. Ed. Engl. 1997, 32, 568-570 (b) Hua, D. H.; Lagneau, N. M.; Chen,
Y.; Robben, P. M.; Clapham, G.; Robinson, P. D. J . Org. Chem. 1996,
61, 4508-4509.
(7) (a) Enders, D.; Peters, R.; Lochtman, R.; Runsink, J . Synlett,
1997, 1462-1464. (b) Enders, D.; Peters, R.; Lochtman, R.; Raabe, G.
Angew. Chem., Int. Ed. 1999, 38, 2421-2423. (c) Zhao, G.; Wang, Q.
G.; Mak, T. C. W. Organometallics 1999, 18, 3623-3636.
(8) (a) Sammakia, T.; Latham, H. A.; Schaad, D. R. J . Org. Chem.
1995, 60, 10-11. (b) Nishibayashi, Y.; Uemura, S. Synlett 1995, 79-
81 (c) Richards, C. J .; Damalidis, T.; Hibbs, D. E.; Hursthouse, M. B.
Synlett 1995, 74-76. (d) Sammakia, T.; Latham, H. A. J . Org. Chem.
1996, 61, 1629-1635. (e) Sammakia, T.; Latham, H. A. J . Org. Chem.
1996, 61, 1629. (e) Manoury, E.; Fossey, J . S.; Ait-Haddou, H.; Daran,
J .-C.; Balavoine, G. G. A. Organometallics 2000, 19, 3736-3739.
(9) Nettekoven, U.; Widhalm, M.; Kamer, P. C. J .; van Leeuwen, P.
W. N. M.; Mereiter, K.; Lutz, M.; Spek, A. L. Organometallics 2000,
19, 2299-2309.
(10) (a) Price, D.; Simpkins, N. S. Tetrahedron Lett. 1995, 36, 6135-
6136. (b) Tsukazaki, M.; Tinkl, M.; Roglans, A.; Chapell, B. J .; Taylor,
N. J .; Snieckus, V. J . Am. Chem. Soc. 1996, 118, 685-686. (c)
Nishibayashi, Y.; Arikawa, Y.; Ohe, K.; Uemura, S. J . Org. Chem. 1996,
61, 1172-1174.
(11) (a)Hayashi T.; Mise T.; Fukushima M.; Kagotani M.; Nagashima
N.; Hamada Y.; Matsumoto A.; Kawakami S.; Konishi M.; Yamamoto
K.; Kumada M. Bull. Chem. Soc. J pn. 1980, 53, 1138-1151. (b) Pugin,
B. (Novartis Ltd). PCT Int. Appl. WO 9632,400 (Chem. Abstr. 1997,
126, 8302r). (c) Pugin, B. (Novartis Ltd). Eur. Pat. Appl. EP 729,969,-
400 (Chem. Abstr. 1997, 126, 276188z). (d) Iftime, G.; Daran, J .-C.;
Manoury, E.; Balavoine, G. G. A. Organometallics 1996, 15, 4808-
4815. (e) Iftime, G.; Daran, J .-C.; Manoury, E.; Balavoine, G. G. A.
Angew. Chem., Int. Ed. 1998, 37, 1698-1700. (f) J endralla, H.; Paulus,
E. Synlett 1997, 471.
* Corresponding author. Fax: 00 (33) 5 61 55 30 03. E-mail:
manoury@lcc-toulouse.fr.
(1) For a recent overview see: Togni, A.; Hayashi, T. Ferrocenes;
VCH: Weinheim, 1995.
(2) For recent reviews: (a) Richards, C. J .; Locke, A. J . Tetra-
hedron: Asymmetry 1998, 9, 2377-2407. (b) Balavoine, G. G. A.;
Daran, J .-C.; Iftime, G.; Manoury, E.; Moreau-Bossuet, C. J . Orga-
nomet. Chem. 1998, 567, 191-198. (c) Riant, O.; Kagan, H. B. In
Advances in Asymmetric Synthesis; Hassner, A., Ed.; J ai Press, 1997;
Vol. 2, pp 189-235. (d) Togni, A. Angew. Chem., Int. Ed. Engl. 1996,
35, 1475-1477.
(3) (a) Marquarding D.; Klusaceck, H.; Gokel, G.; Hoffmann, P.; Ugi,
I. J . Am. Chem. Soc. 1970, 92, 5389-5393. (b) Batelle, L. F.; Bau, R.;
Gokel, G. W.; Okayama, R. T.; Ugi, I. K. J . Am. Chem. Soc. 1973, 95,
482-486.
(12) (a) Richards, C. J .; Mulvaney, A. W. Tetrahedron: Asymmetry
1996, 7, 1419-1430. (b) Ahn, K. H.; Cho, C.-W.; Baek, H.-H.; Park, J .;
Lee, S. J . Org. Chem. 1996, 61, 4937-4943. (c) Donde, Y.; Overman,
L. E. J . Am. Chem. Soc. 1999, 121, 2933-2934. (e) Plenio, H.;
Herrmann, J .; Sehring, A. Chem. Eur. J . 2000, 6, 1820-1829.
10.1021/om020462g CCC: $22.00 © 2002 American Chemical Society
Publication on Web 09/11/2002

Notes
Organometallics, Vol. 21, No. 21, 2002 4553
hexasubstituted ferrocenes.15 The occurrence of supple-
mentary groups from the classical 1,2-substitution could
be very valuable for some applications. For example, in
asymmetric catalysis, an additional substitution may
increase the selectivity of the catalytic system16 or allow
the tethering of the ligand on various supports like
dendrimers.17 For some years, our group has been
involved in the development and the search for synthetic
methods leading to various polysubstituted ferrocenes.2b
In this paper, a highly efficient and general method to
obtain 1,2,3-trisubstituted and 1,2,3,1′-tetrasubstituted
ferrocenes with only planar chirality will be presented.
Ta ble 1. F u n ction a liza tion of 2-Su bstitu ted
F er r ocen yl Dioxa n es
entry
R1
R2
product
yield
1
2
3
4
5
6
7
8
SiMe3
SiMe3
SiMe3
SiMe3
PPh2
PPh2
PPh2
PPh2
SiMe3
SnBu3
PPh2
SPh
SiMe3
SnBu3
PPh2
SPh
2a
2b
2c
2d
2e
2f
78%
50%
29%
68%
42%
52%
37%
70%
2g
2h
Sch em e 1
Resu lts a n d Discu ssion
We have found that these diastereoisomerically pure
2-substituted acetals 1, prepared and purified according
to literature process,5 could be selectively transformed
into the corresponding 1,5-substituted acetals 2 by
action of t-BuLi at -78 °C followed by electrophilic
trapping of the lithiated intermediate. The regioselec-
tivity in favor of the functionalization in the 5 position
is complete. No compounds with substitution in the 3
or 1′ position have been observed. Furthermore, no
products of polyfunctionalization have been detected so
far. A direct reaction between tert-butyllitium and a
2-substituted acetal 1, without precomplexation of
t-BuLi on the acetal part prior to the deprotonation step,
would probably occur on the different available protons
of the ferrocenyl moieties without significant selectivity.
So, the high regioselectivity is probably due to the
precomplexation of tert-butyllithium, either on the two
oxygen atoms of the acetal part of the molecule as
already proposed to explain the selective synthesis of
acetals 1 by Kagan et al.5 or on the other oxygen of the
dioxane ring that is not proximal to the methoxymethyl
group. In the first case, because the 2 position is already
substituted, deprotonation can occur only after rotation
of the dioxane ring leading to the attack on the 5
position. In the second case, the base is already proximal
to the hydrogen atom in the 5 position and the same
lithiated compound should be obtained. So, various 1,5-
disubstituted ferrocenylacetals, which are 1,2,3-trisub-
stituted ferrocenes, could be synthesized with fair to
good yields as single enantiomerically pure diastereoi-
somers as shown in Table 1. However, it should be noted
that compounds 2a and 2g with the same R1 and R2
groups have no planar chirality.
Ta ble 2. Hyd r olysis of 2-Disu bstitu ted F er r ocen yl
Dioxa n es
entry
R1
R2
product
yield
1
2
3
4
5
6
7
SiMe3
SiMe3
SiMe3
SiMe3
PPh2
SiMe3
SnBu3
PPh2
SPh
SnBu3
PPh2
SPh
3a
3b
3c
3d
3f
90%
94%
88%
93%
94%
89%
95%
PPh2
PPh2
3g
3h
Sch em e 2
Hydrolysis of these rather hindered dioxanes could
be achieved in a biphasic dichloromethane/water system
in the presence of p-toluenesulfonic acid5b to yield
different aldehydes 3 with excellent yields (see Scheme
1 and Table 2). Compounds 3a and 3g are not chiral,
but aldehydes 3b, 3c, 3d , 3f, and 3h are chiral and
obtained in an enantiomerically pure form.
(13) (a) Hayashi, T.; Yamamoto, A.; Hojo, M.; Kishi, K.; Ito, Y.;
Nishioka, E.; Miura, H.; Yanagi, K. J . Organomet. Chem. 1989, 370,
129-139. (b) Schwink, L.; Knochel, P. Chem. Eur. J . 1998, 4, 950-
968. (c) Kang, J .; Lee, J . H.; Ahn, S. H.; Choi, J . S. Tetrahedron Lett.
1998, 39, 5523-5526. (d) Zhang, W.; Adachi, Y.; Hirao, T.; Ikeda, I.
Tetrahedron: Asymmetry 1996, 7, 451-460. (e) Park, J .; Lee, S.; Ahn,
K. Y.; Cho, C.-W. Tetrahedron Lett. 1996, 37, 6137-6140. (f) Enders,
D.; Klumpen, T. J . Organomet. Chem. 2001, 637-639, 698-709.
(14) Lee, S.; Koh, J . H.; Park, J . J . Organomet. Chem. 2001, 637-
639, 99-106.
Furthermore, these new enantiomerically pure alde-
hydes could be efficiently transformed into 1,2,3,1′-
tetrasubstituted ferrocenes by successive action of N-
methylpiperazide, t-BuLi, and finally an electrophile
(Scheme 2).11d Compound 5 is, as far as we know, the
first example of an enantiomerically pure 1,2,3,1′-
tetrasubstituted ferrocene with four different substi-
tuents. The functionalization of 1,5-disubstituted fer-
rocenecarboxaldehydes (1,2,3-trisubstituted ferrocenes)
has been tried in only two cases up to now but could
probably be easily extended to some other substrates
(15) Kim, S. G.; Cho, S. C. W.; Ahn, K. H. Tetrahedron: Asymmetry
1997, 8, 1023-1026.
(16) (a) Ko¨llner, C.; Pugin, B.; Togni, A. J . Am. Chem. Soc. 1998,
120, 10274-10275. (b) Schneider, R.; Ko¨llner, C.; Weber, I.; Togni, A.
Chem. Commun. 1999, 2415-2416.
(17) (a) Butler, I. R.; Cullen, W. R. Can. J . Chem. 1989, 67, 1851-
1858. (b) Oosterom, G. E. Ph.D. Dissertation, University of Amsterdam
(The Netherlands), 2001.

4554 Organometallics, Vol. 21, No. 21, 2002
Notes
F igu r e 3. Molecular view of complex 3c with atom-
F igu r e 1. Molecular view of 2g with atom-labeling
labeling scheme. Ellipsoids are drawn at 30% probability.
scheme. Ellipsoids represent 30% probability.
0.661(7) Å, respectively. This dioxane ring is twisted by
40.6° with respect to the Cp ring to which it is attached.
The methoxy group is oriented endo toward the Fe, the
O(3) atom being -1.625(6) Å below the Cp ring. The two
Cp rings are nearly eclipsed with a twist angle of 2.6°.
In compound 2h , the P(2) and S(5) atoms are also
displaced from the Cp ring best planes toward the iron
atom by -0.169(3) and -0.087(3) Å, respectively (endo
structure). As observed in other ferrocenyl thioether
derivatives,19 the phenyl substituent on the sulfur atom
is pushed outside from the Fc block. This observation
agrees with the EHMO study carried out on Fe(C5H4-
SMe)2, which favors the out-of-plane exo conformation
of R with respect to the out-of-plane endo.20 The two
phenyl rings attached to phosphorus are also in exo
position with respect to the ferrocene moiety. As in 2g,
the dioxane ring has a chair conformation with C(11)
and C(13) being away from the O(1)-C(12)-C(14)-O(2)
mean plane by -0.63(1) and 0.64(1) Å, respectively, and
it is twisted with respect to the Cp ring by 56.9°. The
two Cp rings have an intermediate conformation with
a twist angle of 14.9°.
As in the previous compounds, the phosphorus atom
in 3c is displaced from the Cp ring best plane toward
the iron atom by -0.1042(6) Å, but the Si atom deviates
from this plane only by 0.027(1) Å. Of the two phenyl
groups, one is exo, C(211), and the other, C(221), is endo
with respect to the Cp ring. The aldehyde group is
slightly twisted by 12.4° from this Cp ring. The angles
around Si(5) range from 106.1(2)° to 114.3(2)°, the slight
distortion observed from ideal tetrahedral geometry may
be related to some steric interaction with the CHO
group. The Si-C(Cp) distance of 1.878(3) Å is identical
within experimental error to related compounds.21 The
two Cp rings are slightly twisted with an angle of 10.4°
with respect to the eclipsed conformation.
F igu r e 2. Molecular view of complex 2h with atom-
labeling scheme. Ellipsoids are drawn at 30% probability.
by the method described above. So, various 1,2,3,1′-
ferrocenes are now potentially available. The main
restriction is the compatibility of both substituents
already present in the 1 or 5 position of the carboxal-
dehyde with the conditions of the functionalization on
the other cyclopentadienyl ring (N-methylpiperazide
and t-BuLi; see ref 11d). So, if some achiral 1,2,3,1′-
tetrasubstituted ferrocenes have already been de-
scribed,17 our method is, to the best of our knowledge,
the only one for synthesizing compounds with four
different groups in an enantiomerically pure form.
Some crystals suitable for X-ray analysis have been
obtained by slow diffusion of hexane into a dichlo-
romethane solution of compounds 2g, 2h , or 3c. Molec-
ular views of these three complexes with atom-labeling
schemes are shown in Figures 1, 2, and 3.
In compound 2g, the two phosphorus atoms are
displaced endo toward the Fe atom (0.099(1) Å for P(2)
and -0.226(1) Å for P(5)). An overall search on the
Cambridge Database points out that this situation
occurred in roughly 45% of the related structures
already reported.18 All phenyl groups point away from
the dioxane moiety. The dioxane ring has a chair
conformation with C(11) and C(13) being away from the
O(1)-C(12)-C(14)-O(2) mean plane by -0.627(4) and
(19) (a) Adeleke, J . A.; Chen, Y. W.; Liu, L. K. Organometallics 1992,
11, 2543-2550. (b) Broussier, R.; Ninoreille, S.; Bourdon, C.; Blacque,
O.; Ninoreille, C.; Kubicki, Marek M.; Gautheron, B. J . Organomet.
Chem. 1997, 561, 85-96.
(20) Broussier, R.; Bourdon, C.; Blacque, O.; Vallat, A.; Kubicki, M.
M.; Gautheron, B. Bull. Soc. Chim. Fr. 1996, 133, 843-851.
(21) (a) Balavoine, G. G. A.; Daran, J .-C.; Iftime, G.; Lacroix, P. G.;
Manoury, E.; Delaire, J . A.; Maltey-Fanton, I.; Nakatani, K.; Di Bella,
S. Organometallics 1998, 18, 21-29. (b) Palitzsch, W.; Pietzsch, C.;
J acob, K.; Edelmann, F. T.; Gelbrich, T.; Lorenz, V.; Puttnat, M.;
Roewer, G. J . Organomet. Chem. 1998, 554, 139-146. (c) Butler, I.
R.; Cullen, W. R.; Rettig, S. J . Organometallics 1986, 5, 1320-1328.
(18) Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993, 8,
31-37.

Notes
In conclusion, we described a new and general method
Organometallics, Vol. 21, No. 21, 2002 4555
silica gel using a pentane/ether mixture (9:1, v/v) to yield 3a
as a red-orange solid (90% yield).
for the synthesis of ferrocenecarboxaldehydes with
substituents in positions 2 and 5. If the two substituents
are different, the aldehydes are chiral and have been
obtained in an enantiomerically pure form. Further-
more, these aldehydes can be transformed by a one-pot
reaction in good yields and with complete selectivity into
1,2,1′-substituted ferrocenecarboxaldehydes, eventually
with three different substituents, meaning 1,2,3,1′-
tetrasubstituted ferrocenes eventually with four differ-
ent substituents, in an enantiomerically pure form if
the compound is chiral.
Cr ysta l Da ta for 2g: [C40H38FeO3P2]; Mr ) 684.49; ortho-
rhombic; space group P212121;
a ) 10.0638(9) Å, b )
14.8937(13) Å, c ) 22.594(2) Å, V ) 3386.5(5) Å3, Z ) 4, Fcalcd
) 1.343 Mg/m3, µ ) 0.578 mm-1, empirical absorption correc-
tion applied, Tmin ) 0.3558, Tmax ) 0.7723; Mo KR radiation;
T ) 180(2) K; æ scan (Stoe IPDS diffractometer); 2θmax ) 52.2°;
reflections collected/unique/used, 33 401/6639(Rint ) 0.113)/
5044(I>2σ(I)); parameters refined, 416; R/ Rw2(I>2σ(I)) )
0.0595/0.1033, R/ Rw2(all data) ) 0.0904/0.1133; GOF ) 1.106;
∆/ σmax ) 0.09; [∆F]min, [∆F]max, -0.42, 0.63; Flack’s parameter
) 0.02(2).
Cr ysta l Da ta for 2h : [C34H33FeO3PS]; Mr ) 608.48; ortho-
rhombic; space group P212121; a ) 8.711(5) Å, b ) 16.986(5)
Å, c ) 19.351(5) Å, V ) 2863(2) Å3, Z ) 4, Fcalcd ) 1.412 Mg/
m3, µ ) 0.690 mm-1, semiempirical absorption correction
applied, Tmin ) 0.6540, Tmax ) 0.7981; Mo KR radiation; T )
160(2) K; æ scan (Stoe IPDS diffractometer); 2θmax ) 49.4°;
reflections collected/unique/used, 25016/4728(Rint ) 0.113)/
3897(I>2σ(I)); parameters refined, 375; R/ Rw2(I>2σ(I)) )
0.0928/0.1962, R/ Rw2(all data) ) 0.1087/0.2055; GOF ) 1.09;
∆/ σmax ) 0.07; [∆F]min, [∆F]max, -0.49, 0.62; Flack’s parameter
) 0.10(5).
Exp er im en ta l Section
Gen er a l P r oced u r es. All of the reactions were carried out
in the absence of air using standard Schlenk techniques and
vacuum-line manipulations. Chlorotrimethylsilane was dis-
tilled on calcium hydride and stored on 3-4 Å molecular
sieves. Ph2PCl was distilled under reduced pressure on car-
borandum and kept on 3-4 Å molecular sieves. Other com-
pounds were used as commercial samples. N-Methylpiperazine
was distilled and stored over sodium carbonate. All solvents
were dried before use. Thin-layer chromatography was carried
out on Merck Kieselgel 60F254 precoated silica gel plates.
Preparative flash chromatography was performed on Merck
Kieselgel. Instrumentation: Bruker AM250 or AMX 400 (1H,
13C, and 31P NMR), Stoe IPDS (X-ray). Elemental analyses
were performed by the Service d’Analyse du Laboratoire de
Chimie de Coordination, Toulouse (France).
Gen er a l P r oced u r e for th e Dep r oton a tion of Aceta ls
2: Syn th esis of (2S,4S)-4-(Meth oxym eth yl)-2-[2,5-bis(tr i-
m eth ylsilyl)fer r ocen yl]-1,3-d ioxa n e, 2a . In a Schlenk tube,
390 mg of (2S,4S,SFc)-4-(methoxymethyl)-2-[2-(trimethylsilyl)-
ferrocenyl]-1,3-dioxane (1a )5 (1 mmol) was dissolved in 5 mL
of anhydrous ether. The yellow solution was cooled to -78 °C,
and then 0.63 mL of a 1.7 M t-BuLi solution in pentane was
added dropwise. The solution was stirred 2 h at -78 °C before
adding 0.5 mL of freshly distilled Me3SiCl (4 mmol). After 15
min stirring at -78 °C, the mixture was allowed to come back
at RT and stirred 2 h at this temperature. Isopropylamine (5
mL) was added, and after an additional 5 min stirring, 5 mL
of a 2 N sodium hydroxide solution in water was injected. The
mixture was extracted with dichloromethane, washed with
brine, dried on sodium sulfate, and evaporated to yield an
orange oil; the crude material was purified by flash chroma-
tography on silica gel using a pentane/ether mixture. 2a (360
mg, 78%) as an orange oil was obtained
Cr ysta l Da ta for 3c: [C26H27FeOPSi]; Mr ) 470.39; ortho-
rhombic; space group P212121; a ) 12.3089(11) Å, b )
12.9052(15) Å, c ) 15.0422(16) Å, V ) 2389.4(4) Å3, Z ) 4,
F
calcd ) 1.308 Mg/m3, µ ) 0.763 mm-1, semiempirical absorption
correction applied, Tmin ) 0.7912, Tmax ) 0.8885; Mo KR
radiation; T ) 160(2) K; æ scan (Stoe IPDS diffractometer);
2θmax ) 52.1; reflections collected/unique/used, 23619/4680(Rint
2
) 0.069)/4041(I>2σ(I)); parameters refined, 274; R/ Rw
-
(I>2σ(I)) ) 0.0347/0.0768, R/ Rw2(all data) ) 0.0454/0.0811;
GOF ) 1.02; ∆/ σmax ) 0.001; [∆F]min, [∆F]max, -0.24, 0.33;
Flack’s parameter ) 0.03(2).
Structure solution and refinement were carried out with the
programs SIR9722 and SHELXL97.23 The absolute configura-
tions were determined by refining the Flack’s enantiopole
parameter.24 Molecular views were realized with the program
ORTEP-III for Windows.25
Ack n ow led gm en t. We are grateful to the CNRS
(France) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures, detailed spectroscopic characterization, and crystal-
lographic information files (CIF) are available free of charge
via the Internet at http://pubs.acs.org.
OM020462G
Gen er a l P r oced u r e for th e Hyd r olysis of Aceta ls 2:
Syn t h esis of 2,5-Bis(t r im et h ylsilyl)fer r ocen eca r b ox-
a ld eh yd e, 3a . In a Schlenk tube to a solution of acetal 2a in
dichloromethane (ca. 0.15 mol L-1) was added 0.7 equiv of
p-toluenesulfonic acid monohydrate and ca. 130 equiv of
deoxygenated water. The mixture was stirred at dichlo-
romethane reflux during 5 h (bath temperature ) 60 °C). After
cooling, the solution was diluted with ether, washed with
water, dried on sodium sulfate, and evaporated to yield the
aldehyde, which was purified by flash chromatography on
(22) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagn,
R. SIR97, a program for automatic solution of crystal structures by
direct methods. J . Appl. Crystallogr. 1999, 32, 115.
(23) Sheldrick, G. M. SHELXL-97, a program for crystal structure
refinement; University of Go¨ttingen: Germany, 1997.
(24) (a) Flack, H. D. Acta Crystallogr., Sect. A 1983, 39, 876. (b)
Bernardinelli, G.; Flack, H. D. Acta Crystallogr., Sect. A 1985, 41, 500.
(25) Farrugia, L. J . ORTEP3 for Windows. J . Appl. Crystallogr.
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